Anthropogenic debris as nest material in three swift species: New insights into the interactions of atmospheric pollution with wildlife.

Plastic pollution has become a global concern, affecting many species around the world. While well-documented for marine ecosystems, the impact of plastic pollution on terrestrial ecosystems is comparatively limited. In fact, only recently have some studies begun to explore the occurrence, pathways, and impacts of plastic in the atmosphere and on terrestrial species. Here, we assess the presence of synthetic material in nests of three swift species breeding in the Western Palearctic: the common swift (Apus apus), the pallid swift (Apus pallidus), and the alpine swift (Tachymarptis melba). Using data from 487 nests spanning 25 colonies and seven European countries, we show that 36.5 % of the examined nests contained anthropogenic materials, mainly plastic debris. Notably, Pallid swifts' nests, with 85 % of the total nests examined with plastic, rank among birds with the highest plastic content in nests. We also demonstrate that the probability of finding plastic in the nest increased substantially with the human footprint of the landscape. Last, we recorded four cases of swifts entangled in their own nest, a low proportion compared to other species studied previously. Our study provides compelling evidence that plastic pollution may also be considered a concern for other terrestrial species, particularly for birds with highly aerial lifestyles, such as other swifts. The correlation with the human footprint suggests that areas with higher human activity contribute more significantly. Moreover, the entanglement cases, although low, indicate a threat to bird health and welfare. To our knowledge, our study is the first to report a direct interaction between floating plastic debris in the atmosphere and any species. Understanding this interaction is key, not only due to the lack of research on the topic, but also because it highlights that plastic pollution is a multifaceted environmental issue affecting various ecosystem categories, and the broader implications of atmospheric plastic circulation on wildlife and ecosystems health.